ABSTRACTHybridization is increasingly recognized as an important evolutionary force. Novel geneti... more ABSTRACTHybridization is increasingly recognized as an important evolutionary force. Novel genetic methods now enable us to address how the genomes of parental species are combined to build hybrid genomes. However, we still do not know the relative importance of contingencies, genome architecture and local selection in shaping hybrid genomes. Here, we take advantage of the genetically divergent island populations of Italian sparrow on Crete, Corsica and Sicily to investigate the predictors of genomic variation within a hybrid taxon. We test if differentiation is affected by recombination rate, selection, or variation in ancestry proportion from each parent species. We find that the relationship between recombination rate and differentiation is less pronounced within hybrid lineages than between the parent species, as expected if purging of minor parent ancestry in low recombination regions reduces the variation available for differentiation. In addition, we find that differentiation...
Hybridization is increasingly recognized as a potent evolutionary force. Though additive genetic ... more Hybridization is increasingly recognized as a potent evolutionary force. Though additive genetic variation and novel combinations of parental genes theoretically increase the potential for hybrid species to adapt, few empirical studies have investigated the adaptive potential within a hybrid species. Here, we investigate factors promoting phenotypic divergence using genomically diverged island populations of the homoploid hybrid Italian sparrow Passer italiae from Crete, Corsica, and Sicily. We address whether genomic contingencies, adaptation to climate or diet best explain divergence in beak morphology. Populations vary significantly in beak morphology, both between and within islands of origin. Temperature seasonality best explains population divergence in beak size. Interestingly, beak shape along all significant dimensions of variation was best explained by annual precipitation, genomic composition and their interaction, suggesting a role for contingencies. Moreover, beak shape...
Male and female mating couples and morphological data in mating pairs from "Klingavälsåns Na... more Male and female mating couples and morphological data in mating pairs from "Klingavälsåns Naturreservat" and "Sövdemölla" (both populations combined, morphological trait data centred to mean zero). Male and female ID:s and date of capture are given (male above the female he was mating with), and value for each of the eight measured morphological traits that we measured. These trait values were used to estimate the strength of assortative mating
Data for C. splendens male population divergence in mate preferences in sympatric (S) and allopat... more Data for C. splendens male population divergence in mate preferences in sympatric (S) and allopatric (A) populations, as shown in Fig. 3B (Svensson et al. 2014). Male mate preferences have been normalized by dividing by the average male response to conspecific C. splendens females (indicated by line at ‘1’ in Fig. 3B). For statistical tests, see legend to Fig. 3B in Svensson et al. (2014)
Microsatellite data for “Sex differences in developmental plasticity and canalization shape popul... more Microsatellite data for “Sex differences in developmental plasticity and canalization shape population divergence in mate preferences”. BayesAss results (presented in Figure 2 in Svensson et al. (2014), as well as FST-analyses, Structure analyses and Microchecker analyses are based on these microsatellite data. The file contains genetic data from 133 individuals from seven study populations and one outgroup consisting of 90 individuals inhabiting populations along the River Loire, France. The genotypes of all damselflies were assayed at 13 microsatellite loci previously isolated for this species (see e.g. J. D. Austin et al., 2011, Mol. Ecol. Resour. 11, 757). Information on population ecology (sympatry or allopatry) is presented in Supporting Table 1 in the Supporting Material (Svensson et al. 2014)
Hybridization is increasingly recognized as a potent evolutionary force. Although additive geneti... more Hybridization is increasingly recognized as a potent evolutionary force. Although additive genetic variation and novel combinations of parental genes theoretically increase the potential for hybrid species to adapt, few empirical studies have investigated the adaptive potential within a hybrid species. Here, we address whether genomic contingencies, adaptation to climate, or diet best explain divergence in beak morphology using genomically diverged island populations of the homoploid hybrid Italian sparrow Passer italiae from Crete, Corsica, and Sicily. Populations vary significantly in beak morphology both between and within islands of origin. Temperature seasonality best explains population divergence in beak size. Interestingly, beak shape along all significant dimensions of variation was best explained by annual precipitation, genomic composition, and their interaction, suggesting a role for contingencies. Moreover, beak shape similarity to a parent species correlates with propo...
SummaryRecent genomic investigations have revealed hybridization to be an important source of var... more SummaryRecent genomic investigations have revealed hybridization to be an important source of variation, the working material of natural selection1,2. Hybridization can spur adaptive radiations3, transfer adaptive variation across species boundaries4, and generate species with novel niches5. Yet, the limits to viable hybrid genome formation are poorly understood. Here we investigated to what extent hybrid genomes are free to evolve or whether they are restricted to a specific combination of parental alleles by sequencing the genomes of four isolated island populations of the homoploid hybrid Italian sparrowPasser italiae6,7. Based on 61 Italian sparrow genomes from Crete, Corsica, Sicily and Malta, and 10 genomes of each of the parent speciesP. domesticusandP. hispaniolensis,we report that a variety of novel and fully functional hybrid genomic combinations have arisen on the different islands, with differentiation in candidate genes for beak shape and plumage colour. There are limit...
Hybridization can result in novel allelic combinations which can impact the hybrid phenotype thro... more Hybridization can result in novel allelic combinations which can impact the hybrid phenotype through changes in gene expression. While mis-expression in F1 hybrids is well documented, how gene expression evolves in stabilized hybrid taxa remains an open question. As gene expression evolves in a stabilizing manner, break-up of co-evolved cis- and trans-regulatory elements could lead to transgressive patterns of gene expression in hybrids. Here, we address to what extent gonad gene expression has evolved in an established and stable homoploid hybrid, the Italian sparrow (Passer italiae). Through comparison of gene expression in gonads from individuals of the two parental species (i.e., house and Spanish sparrow) to that of Italian sparrows, we find evidence for strongly transgressive expression in male Italian sparrows - 22% of testis genes exhibit expression patterns outside the range of both parent species. In contrast, Italian sparrow ovary expression was similar to that of one of ...
The evolution of striking phenotypes on islands is a well-known phenomenon, and there has been a ... more The evolution of striking phenotypes on islands is a well-known phenomenon, and there has been a long-standing debate on the patterns of body size evolution on islands. The ecological causes driving divergence in insular populations are, however, poorly understood. Reduced predator fauna is expected to lower escape propensity, increase body size and relax selection for crypsis in small-bodied, insular prey species. Here, we investigated whether escape behaviour, body size and dorsal coloration have diverged as predicted under predation release in spatially replicated islet and mainland populations of the lizard species Podarcis gaigeae. We show that islet lizards escape approaching observers at shorter distances and are larger than mainland lizards. Additionally, we found evidence for larger between-population variation in body size among the islet populations than mainland populations. Moreover, islet populations are significantly more divergent in dorsal coloration and match their...
When sexually selected traits diverge because of different local selective environments, prematin... more When sexually selected traits diverge because of different local selective environments, premating isolation might arise as a correlated response. However, sexually selected traits might also diverge by stochastic forces. Here, we show that odour-based mate preferences and scent composition have diverged between islet- and mainland populations of Skyros wall lizard, Podarcis gaigeae. We quantified the degree of scent-mediated premating isolation between populations. Islet lizards preferred scent from islet lizards, whereas the mainland populations were less discriminatory. The pheromone compositions differed more between islets than between islet- and mainland populations and did not differ significantly between mainland populations. There was a tendency for population divergence in pheromones to be positively correlated with neutral genetic divergence. This might indicate a role for genetic drift in evolutionary change in these signals and partial decoupling between signals and preferences. Our results suggest that chemical signals and associated mate preferences can diverge through stochastic and selective forces and influence premating isolation.
Although rapid evolution of body size on islands has long been known, the ecological mechanisms b... more Although rapid evolution of body size on islands has long been known, the ecological mechanisms behind this island phenomenon remain poorly understood. Diet is an important selective pressure for morphological divergence. Here we investigate if selection for novel diets has contributed to the multiple independent cases of island gigantism in the Skyros wall lizard (Podarcis gaigeae) and if diet, predation, or both factors best explain island gigantism. We combined data on body size, shape, bite force, and realized and available diets to address this. Several lines of evidence suggest that diet has contributed to the island gigantism. The larger islet lizards have relatively wider heads and higher bite performance in relation to mainland lizards than would be expected from size differences alone. The proportions of consumed and available hard prey are higher on islets than mainland localities, and lizard body size is significantly correlated with the proportion of hard prey. Furthermore, the main axis of divergence in head shape is significantly correlated with dietary divergence. Finally, a model with only diet and one including diet and predation regime explain body size divergence equally well. Our results suggest that diet is an important ecological factor behind insular body size divergence, but could be consistent with an additional role for predation.
ABSTRACTHybridization is increasingly recognized as an important evolutionary force. Novel geneti... more ABSTRACTHybridization is increasingly recognized as an important evolutionary force. Novel genetic methods now enable us to address how the genomes of parental species are combined to build hybrid genomes. However, we still do not know the relative importance of contingencies, genome architecture and local selection in shaping hybrid genomes. Here, we take advantage of the genetically divergent island populations of Italian sparrow on Crete, Corsica and Sicily to investigate the predictors of genomic variation within a hybrid taxon. We test if differentiation is affected by recombination rate, selection, or variation in ancestry proportion from each parent species. We find that the relationship between recombination rate and differentiation is less pronounced within hybrid lineages than between the parent species, as expected if purging of minor parent ancestry in low recombination regions reduces the variation available for differentiation. In addition, we find that differentiation...
Hybridization is increasingly recognized as a potent evolutionary force. Though additive genetic ... more Hybridization is increasingly recognized as a potent evolutionary force. Though additive genetic variation and novel combinations of parental genes theoretically increase the potential for hybrid species to adapt, few empirical studies have investigated the adaptive potential within a hybrid species. Here, we investigate factors promoting phenotypic divergence using genomically diverged island populations of the homoploid hybrid Italian sparrow Passer italiae from Crete, Corsica, and Sicily. We address whether genomic contingencies, adaptation to climate or diet best explain divergence in beak morphology. Populations vary significantly in beak morphology, both between and within islands of origin. Temperature seasonality best explains population divergence in beak size. Interestingly, beak shape along all significant dimensions of variation was best explained by annual precipitation, genomic composition and their interaction, suggesting a role for contingencies. Moreover, beak shape...
Male and female mating couples and morphological data in mating pairs from "Klingavälsåns Na... more Male and female mating couples and morphological data in mating pairs from "Klingavälsåns Naturreservat" and "Sövdemölla" (both populations combined, morphological trait data centred to mean zero). Male and female ID:s and date of capture are given (male above the female he was mating with), and value for each of the eight measured morphological traits that we measured. These trait values were used to estimate the strength of assortative mating
Data for C. splendens male population divergence in mate preferences in sympatric (S) and allopat... more Data for C. splendens male population divergence in mate preferences in sympatric (S) and allopatric (A) populations, as shown in Fig. 3B (Svensson et al. 2014). Male mate preferences have been normalized by dividing by the average male response to conspecific C. splendens females (indicated by line at ‘1’ in Fig. 3B). For statistical tests, see legend to Fig. 3B in Svensson et al. (2014)
Microsatellite data for “Sex differences in developmental plasticity and canalization shape popul... more Microsatellite data for “Sex differences in developmental plasticity and canalization shape population divergence in mate preferences”. BayesAss results (presented in Figure 2 in Svensson et al. (2014), as well as FST-analyses, Structure analyses and Microchecker analyses are based on these microsatellite data. The file contains genetic data from 133 individuals from seven study populations and one outgroup consisting of 90 individuals inhabiting populations along the River Loire, France. The genotypes of all damselflies were assayed at 13 microsatellite loci previously isolated for this species (see e.g. J. D. Austin et al., 2011, Mol. Ecol. Resour. 11, 757). Information on population ecology (sympatry or allopatry) is presented in Supporting Table 1 in the Supporting Material (Svensson et al. 2014)
Hybridization is increasingly recognized as a potent evolutionary force. Although additive geneti... more Hybridization is increasingly recognized as a potent evolutionary force. Although additive genetic variation and novel combinations of parental genes theoretically increase the potential for hybrid species to adapt, few empirical studies have investigated the adaptive potential within a hybrid species. Here, we address whether genomic contingencies, adaptation to climate, or diet best explain divergence in beak morphology using genomically diverged island populations of the homoploid hybrid Italian sparrow Passer italiae from Crete, Corsica, and Sicily. Populations vary significantly in beak morphology both between and within islands of origin. Temperature seasonality best explains population divergence in beak size. Interestingly, beak shape along all significant dimensions of variation was best explained by annual precipitation, genomic composition, and their interaction, suggesting a role for contingencies. Moreover, beak shape similarity to a parent species correlates with propo...
SummaryRecent genomic investigations have revealed hybridization to be an important source of var... more SummaryRecent genomic investigations have revealed hybridization to be an important source of variation, the working material of natural selection1,2. Hybridization can spur adaptive radiations3, transfer adaptive variation across species boundaries4, and generate species with novel niches5. Yet, the limits to viable hybrid genome formation are poorly understood. Here we investigated to what extent hybrid genomes are free to evolve or whether they are restricted to a specific combination of parental alleles by sequencing the genomes of four isolated island populations of the homoploid hybrid Italian sparrowPasser italiae6,7. Based on 61 Italian sparrow genomes from Crete, Corsica, Sicily and Malta, and 10 genomes of each of the parent speciesP. domesticusandP. hispaniolensis,we report that a variety of novel and fully functional hybrid genomic combinations have arisen on the different islands, with differentiation in candidate genes for beak shape and plumage colour. There are limit...
Hybridization can result in novel allelic combinations which can impact the hybrid phenotype thro... more Hybridization can result in novel allelic combinations which can impact the hybrid phenotype through changes in gene expression. While mis-expression in F1 hybrids is well documented, how gene expression evolves in stabilized hybrid taxa remains an open question. As gene expression evolves in a stabilizing manner, break-up of co-evolved cis- and trans-regulatory elements could lead to transgressive patterns of gene expression in hybrids. Here, we address to what extent gonad gene expression has evolved in an established and stable homoploid hybrid, the Italian sparrow (Passer italiae). Through comparison of gene expression in gonads from individuals of the two parental species (i.e., house and Spanish sparrow) to that of Italian sparrows, we find evidence for strongly transgressive expression in male Italian sparrows - 22% of testis genes exhibit expression patterns outside the range of both parent species. In contrast, Italian sparrow ovary expression was similar to that of one of ...
The evolution of striking phenotypes on islands is a well-known phenomenon, and there has been a ... more The evolution of striking phenotypes on islands is a well-known phenomenon, and there has been a long-standing debate on the patterns of body size evolution on islands. The ecological causes driving divergence in insular populations are, however, poorly understood. Reduced predator fauna is expected to lower escape propensity, increase body size and relax selection for crypsis in small-bodied, insular prey species. Here, we investigated whether escape behaviour, body size and dorsal coloration have diverged as predicted under predation release in spatially replicated islet and mainland populations of the lizard species Podarcis gaigeae. We show that islet lizards escape approaching observers at shorter distances and are larger than mainland lizards. Additionally, we found evidence for larger between-population variation in body size among the islet populations than mainland populations. Moreover, islet populations are significantly more divergent in dorsal coloration and match their...
When sexually selected traits diverge because of different local selective environments, prematin... more When sexually selected traits diverge because of different local selective environments, premating isolation might arise as a correlated response. However, sexually selected traits might also diverge by stochastic forces. Here, we show that odour-based mate preferences and scent composition have diverged between islet- and mainland populations of Skyros wall lizard, Podarcis gaigeae. We quantified the degree of scent-mediated premating isolation between populations. Islet lizards preferred scent from islet lizards, whereas the mainland populations were less discriminatory. The pheromone compositions differed more between islets than between islet- and mainland populations and did not differ significantly between mainland populations. There was a tendency for population divergence in pheromones to be positively correlated with neutral genetic divergence. This might indicate a role for genetic drift in evolutionary change in these signals and partial decoupling between signals and preferences. Our results suggest that chemical signals and associated mate preferences can diverge through stochastic and selective forces and influence premating isolation.
Although rapid evolution of body size on islands has long been known, the ecological mechanisms b... more Although rapid evolution of body size on islands has long been known, the ecological mechanisms behind this island phenomenon remain poorly understood. Diet is an important selective pressure for morphological divergence. Here we investigate if selection for novel diets has contributed to the multiple independent cases of island gigantism in the Skyros wall lizard (Podarcis gaigeae) and if diet, predation, or both factors best explain island gigantism. We combined data on body size, shape, bite force, and realized and available diets to address this. Several lines of evidence suggest that diet has contributed to the island gigantism. The larger islet lizards have relatively wider heads and higher bite performance in relation to mainland lizards than would be expected from size differences alone. The proportions of consumed and available hard prey are higher on islets than mainland localities, and lizard body size is significantly correlated with the proportion of hard prey. Furthermore, the main axis of divergence in head shape is significantly correlated with dietary divergence. Finally, a model with only diet and one including diet and predation regime explain body size divergence equally well. Our results suggest that diet is an important ecological factor behind insular body size divergence, but could be consistent with an additional role for predation.
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